1. Field of the Invention
This invention relates to encoding apparatus and to methods associated with these. More particularly, the invention relates to application of acoustic methods to encoding keyboards. The present application is an improvement of the acoustic method disclosed in my copending application Ser. No. 853,778 filed Nov. 21, 1977 and having the same assignee. To the extent appropriate to the present invention, the disclosure of that application is incorporated herein by reference.
2. Description of the Prior Art
Encoding apparatus for use with many and varied types of equipment have long been known. Yet, there is a continued search for encoders having both low cost and high reliability.
One well-known type of encoding keyboard makes use of light beams in parallel channels and key-operated code levers which are oriented at right angles to the channels and can be placed in a position to block the beams of light in selected ones of the channels, e.g., as disclosed in U.S. Pat. No. 3,032,163. Such equipment requires a multiplicity of light sources and a multiplicity of sensor elements. The light sources and the sensor elements are all relatively expensive and require additional power sources, the light sources in particular consuming appreciable power. Furthermore, if one of the light sources fails, or, worse yet, if the power supply for the light sources fails, there is no way of operating the system even if all the sensors are in good condition.
An encoding apparatus based on use of acoustical wave fronts in rods has been disclosed in the above-mentioned copending application and specifically applied to a keyboard. The technique disclosed there is based on determination of an elapsed time. That approach is self-powered and self-strobed and requires no electrical or mechanical power sources for generating the code signals. A source of power is necessary, of course, for the electronic elements (electronic counters and logic circuitry) required for determining the elapsed time and expressing it as code corresponding to the key depressed. While it is a considerable improvement over known art, this last keyboard has significant limitations. For instance, if the code for the keys must be different from the output of the counters (usually binary), then a ROM ("read only memory") must be provided for conversion of the counter output to a desired code. Furthermore, though the above-mentioned keyboard making use of a single acoustic rod is simpler and cheaper than prior art keyboards, there is still a need for less logic circuitry and simpler and less critical input circuitry. In addition, it has been found that an encoding apparatus based upon elapsed time determinations on acoustic waves of the type disclosed in the copending application is somewhat sensitive to mechanical tolerances, striker wear, and temperature variations. Accordingly, there is need for an even more economical, highly reliable encoding apparatus having even less parts subject to failure and requiring even less power to operate.